1. Field of the Invention
The present invention relates to manufacture of electrical circuitry and, more particularly, concerns manufacture of electrical circuitry by fully additive electroforming processes.
2. Description of Related Art
Printed electrical circuits, including both rigid and flexible printed electrical circuits, generally comprise a pattern of electrical conductors or conductive traces carried by and bonded to a dielectric. Printed circuitry, at present, whether flexible circuits or circuits on relatively rigid boards, is made by well known etching processes. Conventional steps employed in such etching processes include covering a dielectric substrate with a coat of conductive material, such as copper, which will form the traces of the circuit, and then coating the copper with a resist. Artwork in the form of a mask having a pattern of optically-opaque and optically-transmissive portions formed therein is applied over the resist, and the latter is then optically exposed through the mask so that portions of the resist which have been exposed to light may be developed. Those portions of the resist which have not been exposed and developed are then removed to leave a positive pattern of resist on the copper surface. The assembly of substrate, copper and positive pattern of resist is then subjected to etching fluids which do not affect the resist but which remove the copper in areas not covered by resist. The developed resist is then stripped to provide the desired pattern of copper conductors or traces bonded to the dielectric substrate.
Conventional etched circuit processes have a number of disadvantages. Dimensional precision is difficult to achieve. The use of various etching, stripping and cleaning fluids require special handling of hazardous chemicals. Techniques for disposal of the resulting effluents are complex and expensive, and subject to strict government controls. Etched circuit processing has a relatively low yield, greatly increasing the cost of the processing, which inherently involves a large number of costly processing steps.
Plating mandrels have been employed in the past for the manufacture of relatively large parts. Such mandrels are formed in desired configurations, and then a part, such as, for example, an internally finned waveguide, is electroplated upon the mandrel. After the electroplating, the part is separated from the mandrel. The mandrel may be dissolved if it is located in the interior of the part that is made. However, such mandrels have not been employed for the manufacture of electrical circuitry, nor for laminating electroplated components to another medium or substrate.
Accordingly, it is an object of the present invention to provide methods and apparatus for manufacture of electrical circuitry employing permanent mandrels, and which avoid problems attendant upon etched circuit processing.